You should check the Revision section near the
title section to ensure that the indicated changes were
made in the drawing itself. You must ensure that the
construction plan, the specifications, and the
drawings are discussing the same project. When there
are inconsistencies between general drawings and
details, details should be followed unless they are
When there are inconsistencies
between drawings and specifications, you should
follow the specifications.
As an estimator, you must first study the
specifications and then use them with the drawings
when preparing quantity estimates.
become thoroughly familiar with all the requirements
stated in the specifications.
Some estimators may
have to read the specifications more than once to fix
these requirements in their mind. You are encouraged
to make notes as you read the specifications. These
notes will be helpful to you later as you examine the
drawings. In the notes, list any unusual or unfamiliar
items of work or materials and reminders for usc
during examination of the drawings. A list of
activities and materials that are described or
mentioned in the specifications is helpful in checking
The tables and diagrams in the Seabee Planners
and Estimators Handbook, NAVFAC P-405, should
save you time in preparing estimates and, when
understood and used properly, provide accurate
Whenever possible, the tables and the
diagrams used were based on Seabee experience.
Where suitable information was not available,
construction experience was adjusted to represent
production under the range of conditions encountered
in Seabee construction. A thorough knowledge of the
project drawings and specifications makes you alert to
the various areas where errors may occur.
Accuracy as a Basis for Ordering and
Quantity estimates are used as a basis for
purchasing materials, determining equipment, and
determining manpower requirements. They are also
used in scheduling progress, which provides the basis
for scheduling material deliveries, equipment, and
manpower. Accuracy in preparing quantity estimates
is extremely important; these estimates have
widespread uses and errors can be multiplied many
times. Say, for example, a concrete slab is to measure
100 feet by 800 feet. If you misread the dimension for
the 800-foot side as 300 feet, the computed area of the
slab will be 30,000 square feet, when it should
actually be 80,000 square feet. Since area is the basis
for ordering materials, there will be shortages. For
example, concrete ingredients, lumber, reinforcing
materials, and everything else involved in mixing and
placing the concrete, including equipment time,
manpower, and man-hours, will be seriously
underestimated and ordered.
The need for accuracy is vital, and quantity
estimates should be checked to eliminate as many
errors as possible. One of the best ways to check your
quantity estimate is to have another person make an
independent estimate and then to compare the two.
Any differences should be checked to determine
which is right. A less effective way of checking is for
another person to take your quantity estimate and
check all measurements, recordings, computations,
extensions, and copy work, keeping in mind the most
common error sources (listed in the next section).
Failure to read all the notes on a drawing or
failure to examine reference drawings results in many
For example, you may overlook a note
that states symmetrical about the center line and
thus compute only half the required quantity.
Errors in scaling obviously mean erroneous
quantities. Great care should be taken in scaling
drawings so correct measurements are recorded.
Common scaling errors include using the wrong
scale, reading the wrong side of a scale, and failing to
note that a detail being scaled is drawn to a scale
different from that of the rest of the drawing.
Remember: Some drawings are not drawn to scale.
Since these cannot be scaled for dimensions, you must
obtain dimensions from other sources.
Sometimes wrongly interpreting a section of the
specifications causes errors in the estimate. If there is
any doubt concerning the meaning of any part of
the specification, you should request an explanation
of that particular part.
Omissions are usually the result of careless
examination of the drawings. Thoroughness in
examining drawings and specifications usually
eliminates errors of omission. Checklists should be
used to assure that all activities or materials have been
included in the estimate. If drawings are revised after
material takeoff, new issues must be compared with